A variety of products are formed by compressing a loose granular or powder material into a cake, tablet, or other shape which has sufficient integrity to retain its compressed shape. For instance, in the preparation of pharmaceuticals taking the form of pressed tablets, an active ingredient is dispersed in a matrix or carrier such as glucose, sucrose, dextrose, polysaccharide, or the like, to form a loose powdered or granular feedstock. A selected quantity of the feedstock is deposited into a mold or die cavity, and a pair of punches, each having a recess or depression formed in its face in the negative image of one-half of a desired tablet shape, are brought together in the die cavity so as to compress the feedstock between the punches to form a tablet. Typically, one of the punches is then withdrawn from the die cavity through an open end thereof, and the tablet is removed from the die.
A persistent and vexing problem in the manufacture of compression-molded products is sticking of the compressed tablet to the punches. This can result in a number of undesirable consequences. For example, sticking can hinder removal of the product from the die. Furthermore, even if the product is successfully removed from the die, a portion of the outer surface of the product can remain adhered to a punch, resulting in a defect or "dimple" in the product.
A number of approaches have been used to reduce the sticking of product to the punches. For instance, a lubricant is sometimes added to the feedstock. Alternatively, a lubricant or release material is sometimes applied to the faces of the punches. While these approaches are somewhat effective in dealing with the sticking problem, they necessitate use of additional materials which represent added cost in the manufacturing operation.
Another problem associated with the tooling used for making compression-molded products is the building up of deposits of the feedstock material on the inner surface of the die over repeated uses. In many cases, the die must be cleaned frequently in order to prevent malfunctioning of the tooling caused by a build-up of feedstock, particularly with certain types of feedstock such as dextrose or the like. This need for frequent cleaning results in frequent downtime, thus decreasing manufacturing efficiency.